Classified information may be leaked when an unauthorized person illegally accesses and prints scanned data that was obtained by scanning confidential documents, for example, and Japanese Patent-Application Publication No. 2006-211264 discloses a printing system capable of preventing such classified information leakage. More specifically, a confidential document contains public key information, and an image reading device extracts the public key information when scanning the confidential document and encrypts resultant scanned data by using the extracted public key information. If an unauthorized person illegally accesses the scanned data, a printing device does not print the scanned data unless the scanned data is decrypted.